This invention relates to the art of polybenzoxazole (PBO) polymers.
Polybenzoxazoles are a class of polymers within the larger class of polybenzazoles. Polybenzazoles (PBZ) are generally classified as AB-polymers, containing a plurality of mer units depicted in formula 1(a), or AA/BB, containing a plurality of mer units which conform with formula 1(b) ##STR1## wherein:
each Ar is an aromatic group,
DM is a divalent organic moiety which is and inert in acid under polymerization conditions,
each Z is either --O--, --S-- or --NR--, wherein R is a hydrogen atom or an aromatic moiety which is stable under PBZ synthesis and processing conditions and does not interfere with the synthesis or later use of the polymer.
(For the purpose of this application, when the nitrogen atoms and Z moieties of a mer unit are depicted as bonded to an aromatic group without indicating their position, as in Formulae 1(a)-(b), it shall be understood that:
(1) nitrogen atoms and Z moieties in an azole ring are bonded to the aromatic group in ortho position with respect to each other; and PA1 (2) if the mer unit contains two azole rings, one nitrogen atom and Z moiety may be in either cis-position or trans-position with respect to the other nitrogen atom and Z moiety, as described and illustrated in 11 Ency. Poly. Sci. & Eng., supra, at 602, which is incorporated herein by reference.) PA1 (1) a primary amine group bonded to the aromatic group and PA1 (2) a hydroxy, thiol or primary or secondary amine group bonded to an aromatic carbon atom ortho to said primary amine group. PA1 (1) an aromatic group: PA1 (2) two o-amino-hydroxy moieties bonded to said aromatic group; and PA1 (3) a methyl group bonded to said aromatic group. The aromatic group and o-amino-hydroxy moieties have the meaning and preferred embodiments previously defined. The aromatic ring must be chosen such that it may be bonded to the five substituent groups described, i.e., it may be a pyridinyl moiety but not a pyrimidinyl moiety The aromatic group is highly preferably a six-membered ring and most preferably a phenylene moiety. PA1 (1) reacting an aromatic diol having a pendant methyl group, such as 2-methylresorcinol or 2-methylhydroquinone, with an alkyl haloformate under conditions such that a dicarbonate is formed: PA1 (2) contacting the dicarbonate with nitric and sulfuric acids to nitrate it ortho to the ester moieties; PA1 (3) converting the nitrated dicarbonate back to a nitrated diol, for instance by hydrolysis with lower alkanols in the presence of acids: and PA1 (4) hydrogenating the nitro groups on the diol, such as catalytically or electrolytically. All four reactions are known individually in the art. The formation of dicarbonates is described in Meyers et al., 1978 Tetrahedron Letters 1375 (1978). Suitable nitration and reduction conditions are described in G. M. Loudon, Organic Chemistry 590, 596-610, and 1197 (Addison-Wesley Publ. Co. 1984): Lysenko, High Purity Process for the Preparation of 4,6-Diamino-1,3-Benzenediol, U.S. Pat. No. 4,766,244 (Aug. 23, 1988) and Gregory et al., Electrochemical Synthesis of Substituted Aromatic Amines in Basic Media, U.S. Pat. No. 4,764,263 (Aug. 16, 1988) which are incorporated by reference. The synthesis is more specifically described in U.S. patent application Ser. No. 290,068 (filed Dec. 27, 1988), which is incorporated herein by reference.
In polybenzoxazole polymers, each Z group is an oxygen atom.
Polybenzazoles are synthesized by the reaction of one or more difunctional monomers, each of which contains at least two functional moieties chosen from the group consisting of electron-deficient carbon groups and o-amino-basic moieties. Such reactions are illustrated in formulae 2(a) and (b). ##STR2## wherein each Q is an electron-deficient carbon group and all other moieties have the meaning and preferred embodiments previously given. The divalent organic moiety DM ordinarily comprises an aromatic group.
Polybenzazole polymers, their properties and their synthesis are discussed in detail in the following references: Sybert et al., Liquid Crystalline Polymer Compositions, Process and Products, U.S. Pat. No. 4,772,678 (Sept. 20, 1988): Wolfe et al., Liquid Crystalline Polymer Compositions, Process and Products, U.S. Pat. No. 4,703,103 (Oct. 27, 1987): Wolfe et al., Liquid Crystalline Polymer Compositions, Process and Products, U.S. Pat. No. 4,533,692 (Aug. 6, 1985): Wolfe et al., Liquid Crystalline Poly(2,6-Benzothiazole) Compositions, Process and Products, U.S. Pat. No. 4,533,724 (Aug. 6, 1985); Wolfe, Liquid Crystalline Polymer Compositions, Process and Products, U.S. Pat. No. 4,533,693 (Aug. 6, 1985): Imai et al. "Polybenzoxazoles and Polybenzothiazoles," 83 Makromol. Chem. 167 (1965), Evers, Thermoxadatively Stable Articulated p-Benzobisoxazole and p-Benzobisthiazole Polymers, U.S. Pat. No. 4,359,567 (Nov. 16, 1982); Tsai et al., Method for Making Heterocyclic Block Copolymer, U.S. Pat. No. 4,578,432 (Mar. 25, 1986) and 11 Ency. Poly. Sci. & Eng., Polybenzothiazoles and Polybenzoxazoles, 601 (J. Wiley & Sons 1988), which are incorporated herein by reference.
Polybenzazoles are soluble in strong acids. However, they are substantially unreactive, and do not provide reactive sites to permit modification of the polymer properties, such as cross-linking to decrease solubility in acids. What are needed are monomers and polybenzoxazole polymers or copolymers which provide reactive sites.